exo: Implement zcr_linux_explicit_synchronization_v1

components/exo/surface.h

Index: components/exo/surface.h
diff --git a/components/exo/surface.h b/components/exo/surface.h
index a3706787e488021f0d164a800f35417e2bcdaa6f..e6ef4f25d8519d95beb6da968e1063767c3a927d 100644
--- a/components/exo/surface.h
+++ b/components/exo/surface.h
@@ -23,6 +23,7 @@
 #include "ui/compositor/compositor.h"
 #include "ui/compositor/layer_owner_delegate.h"
 #include "ui/gfx/geometry/rect.h"
+#include "ui/gfx/gpu_fence.h"
 
 namespace base {
 namespace trace_event {
@@ -109,6 +110,11 @@ class Surface : public ui::LayerOwnerDelegate,
   // to one surface at a time.
   void Attach(Buffer* buffer);
 
+  // Provide an acquire-fence (as a raw file descriptor) for the next surface

[reveman, 2016/10/09 19:03:17]

nit: update comment as this is not a raw file descriptor but instead the
abstract GpuFence class.

[fooishbar, 2016/10/12 15:41:56]

Done.

+  // commit. A buffer must be attached in the same transaction as applying a

[reveman, 2016/10/09 19:03:17]

What happens if a client doesn't respect this? We can't trust the client to do
the right thing so we need to make sure we do something reasonable if misused.

[fooishbar, 2016/10/12 15:41:56]

Probably the same which happens if 'A buffer can only be attached to one surface
at a time' is violated? We can kill the client (harsh, but gets the point across
quickly), or use the first one (discarding others), or the last. I have no real
preference for which would be best.

+  // fence.
+  void FenceAcquire(std::unique_ptr<gfx::GpuFence> fence);

[reveman, 2016/10/09 19:03:17]

nit: s/FenceAcquire/SetAcquireFence/. We try to match the wayland interfaces in
terms of naming as much as possible in exo code.

[fooishbar, 2016/10/12 15:41:56]

Done.

+
   // Describe the regions where the pending buffer is different from the
   // current surface contents, and where the surface therefore needs to be
   // repainted.
@@ -333,6 +339,9 @@ class Surface : public ui::LayerOwnerDelegate,
   // The buffer that will become the content of surface when Commit() is called.
   BufferAttachment pending_buffer_;
 
+  std::unique_ptr<gfx::GpuFence> acquire_fence_;

[reveman, 2016/10/09 19:03:17]

nit: can you move acquire_fence_ just below current_buffer_ on line 382 and keep
pending_acquire_fence_ here as now.
nit: a short comment in both cases similar to other pending/active state would
be nice for consistency.

[fooishbar, 2016/10/12 15:41:56]

Done.

+  std::unique_ptr<gfx::GpuFence> pending_acquire_fence_;
+
   cc::SurfaceManager* surface_manager_;
 
   scoped_refptr<SurfaceFactoryOwner> factory_owner_;